Metallic blasting and abrasive material



Patented Oct. 15, 1940 UNITED STATES METALLIC BLASTIN G AND ABRASIVE MATERIAL Oscar E. Harder, Columbus, Ohio, assignor, by mesne assignments, to The Globe Steel Abrasive Company, Mansfield, Ohio, a corporation of Ohio No Drawing. Application December 7, 1939, Serial No. 308,050

7 Claims.

My invention relates to metallic blasting and abrasive material. It has to do particularly with chilled iron particles which are used for cutting, grinding and polishing in the stone industry and for surface cleaning, scale and metal removal in various industries. It is particularly useful in connection with the cleaning of surfaces, scale and metal removal in various metal processing industries, though it is 'not necessarily limited thereto.

It is old in the art of sawing, boring or polishing various types of rock, glass, terra cotta, etc., to employ spherical-shaped metal particles, termed shot as the abrasive media. The essential properties of the shot for such applications are, hardness and toughness. The hardness should be such that the material is relatively resistant to Wear, and not readily flattened nor indented by pressure. The toughness should be such that the material is relatively resistant to fracturing when subjected to impact or crushing stress. With breakage of the shot in service, the fragmented shot must be removed from the stone cutting or polishing equipment and a new supply introduced. This is expensive and causes delay in production.

It is also old in the art of metal blasting, in which a medium is impacted by mechanical means or air pressure against the metal surfaces to be cleaned, to use metal shot and crushed metal particles or metal grit as the blasting medium. For certain metal cleaning and metal removal processes a blasting medium with a high degree of hardness is desirable to eiiect the desired cutting action, while a relatively high toughness or resistance to fracturing on impact is highly essential since on breaking up the particles become too finely divided for satisfactory service performance.

Shot produced by granulation of molten metal, of cast iron analysis, by various processes have been used extensively as abrasive and blasting materials by the granite and metal blastingindustrie's. Angular -grit, produced by fracturing the oversize shot which are too large for use in the present processes, is at times employed as a metal blasting medium. Such material is frequently referred to in the trade as steel shot or grit although it is actually of the chemical composition usually referred to as cast iron, but due to the rapid chilling induced by the granulating process usually. has the microstructure which is characteristic of white or chilled cast-iron.

One method of granulating cast iron in the production of shot consists of directing a stream of Water under pressure against a thinstream of the molten metal and letting the resulting small particles fall into a tank of water. A desirable feature is that the molten metalis con- 5 verted into small round particles and cooled rapidly.

The ordinary chilled iron of commerce has high hardness but tends to be brittle and readily breakable into fragments when subjected to impact stress. In recent years, the industry has been earnestly endeavoring to obtain an abrasive or blasting material of high crushing strength and high impact resistance. Cost of the material is an important consideration and, on that basis, cast iron is one of the most suitable materials. j

Other investigators have indicated their be lief that the toughness of blasting material of this general type may be improved by incorporating with a relatively high carbon ferrous base alloy two or more alloying elements such as chromium and vanadium, chromium and molybdenum and chromium with nickel and molybdenum. These alloying elements are relatively expensive. Furthermore, they have an economic disadvantage in that oxidation losses occur with most of them when they are charged directly into the cupola. I

One of the objects of this invention is to provide metallic blasting and abrasive material in the .form of shot or grit particles which is equal to prior art material with respect to hardness and wear resistance, but which is superior toprior art material, both from the standpoint 35 of resistance to crushing under compression loading, and of resistance to fracturing under impact.

Another object of this invention is to provide a metallic blasting and abrasive material which is relatively hard and resistant to wear and not readily fractured nor flattened when subjected to impact or crushing stress,- thus improving the service life of the shot or grit and reducing expense and delays in production as well as providing more effective service.

Another object of this invention is to produce shot or grit of the type indicated with increased toughness and compressive strength without the use of relatively expensive alloying elements and without the disadvantages resulting from those oxidation losses which occur when such elements as chromium, vanadium and molybdenum are used. 1

It is an object of this invention to produce 55 chilled cast iron particles which will give better performance in service where a certain amount of impact is encountered as in the granite cutting and metal blasting industry.-

I have discovered that chilled iron particles of the ordinary composition of the cast iron of commerce but containing an apportioned addition of copper, are of materially improved resistance to crushing pressure and to fracturing under impact over the ordinary chilled iron. Other alloying elements such as chromium, vanadium, nickel and molybdenum are relatively expensive in comparison with the inexpensive copper addition of my invention. The use of copper as an alloying element also has a further economic advantage in that no oxidation losses of copper'occur when it is charged directly into the cupola. As a matter of fact, it is not economically feasible to charge-the above-mentioned alloying elements, with the exception of nickel, directly into the cupola. Hence, it is customary to add such alloying elements to the metal after it has been tapped from the cupola into a ladle. Since the copper addition of my invention can be added directly to the cupola charge without loss of the copper, it is possible to closely control the composition and employ a continuous tapping and granulating process. Generally speaking, the abrasive and blasting chilled iron particles of my invention are made of a copper-containing high-carbon ferrous-base alloy containing special amounts of copper, varying from about 0.2 per cent to 3.0 per cent cop- I have discovered that a copper content within the special range of about 0.2 per cent to 3.0 per cent copper has provided highly satisfactory results when used in conjunction with iron alloys quite similar in composition to what is generally thought of by those skilled in the art as gray cast iron. However, the abrasive and blasting material of my invention differs structurally from gray cast iron by virtue of the rapid rate of solidification and cooling induced by the granulation processes used to form the shot product. The structural constituents of white or chilled iron are largely cementite (FezC) and the various transformation products of austenite. The composition range of cast iron to which I refer as being especially improved by the addition of copper in the range of about .2 to 3 per cent isas follows:

Carbon About .10

While approximate contents are given for the manganese, phosphorus and sulfur, these elements are not critical in the composition of my material and may be varied over a considerable range without materially affecting the desirable properties, as for instance, manganese 0.2 to phosphorus .03 to 1.0% and sulfur .03 to The element of cost of raw material is an important factor and I prefer to take advantage of the relatively low price at which cast iron scrap may be purchased and utilized in melting. Cast iron scrap may q'ontain some small amounts of alloying elements such as are used in industry but these do not interfere with the utilization of commercial scrap in the production of my imin the claims in the expression and the balance substantially iron."

I have found that a somewhat better product is produced when copper in my preferred range is added to a base material of somewhat narrower composition limits such as carbon from 2.90 to 3.40 per cent and silicon from 1 per cent to 1.75 per cent.

I have also found that even small additions of copper of the order of one-fourth per cent increase the resistance of chilled iron to fracture in compression and impact tests, but for more marked improvement in toughness, one-half per cent or more of copper is required. The upper limit of about 3 per cent is the preferred maximum copper content.

The composition of the chilled iron of my invention is the same whether the material is to be used in stone cutting and polishing, or the metal blasting industries.

In the numerous comparative laboratory tests which have been conducted on shot of prior art production and the copper-bearing shot of my of the shot of each type were the same, theweight of the hammer and its height of fall were kept constant so that the data are strictly comparable.

Numerous other similar laboratory tests have shown the copper-bearing shot of my invention --1 to withstand from 22 per cent to 49 per cent more impact blows before fracture than prior art shot.

(WEIGHT OF HAMMER-2.16 POUNDS. HEIGHT OF FALL-O.45")

Average number of blows to fracture g igg g Shot diameter coppepbcaring Test 2213s Test arose-n f Percent Average 36 The shot of sample 52639-D contained 0.56 per cent copper by analysis, while the shot of sample 22138 was similar in all respects except that it contained no added copper.

The copper-bearing shot of my invention has also been found by laboratory test to withstand from 5 to 10 per cent greater loads before fracturing in static compression tests than the prior art shot material. Tests have shown that the shot produced in accordance with my invention have a hardness of at least 550 on the Brinell scale or its equivalent.

Commercial use of my copper-bearing shot has shown that the useful life in metal blasting is materially increased over former materials and over current competitive materials. This was to be expected from the laboratory tests. There are decided advantages in having a shot which does not fracture too readily or which lastslonger before it becomes so fine that it has to be. dis* ca ded.

In producing the new copper-containing chilled iron, it is not necessary to make any changes from the conventional cupola furnacing methods. The requisite quantity of copper is added to each charge and practically no loss is encountered in the melting operation. The copper may be added as virgin metal, but is preferably added as the less expensive scrap copper commercially available.

The important features of my invention are the fact that the special additions of from 0.2 per cent to 3 per cent copper will improve the impact and crushing strength of chilled iron shot with little or no alteration of the hardness or microstructure. Since no change in the conventional cupola practice need be made, and since but minor amounts of the relatively inexpensive copper are used, the invention is economically feasible. My process sacrifices none of the desirable characteristics of the cast iron materials which have found extensive use in the granite and metal blasting industries while it enhances the impact and crushing resistance of the material and thus increases the service performance of the material both in the form of shot and grit.

Having thus described .my invention, what I claim is:

1. Metallic blasting and abrasive material formed of chilled iron base particles containing at least .2 per cent copper as an alloying element, said material having a hardness of at least 550 Brinell. I

2. Metallic blasting. and abrasive material comprising particles formed of chilled iron hav-' ing a carbon content ranging from 2.9 to 3.6 per cent and containing copper as an alloying element in the percentage from .2 to 3.0 per cent.

3. Metallic blasting and abrasive material comprising chilled iron particles containing from 2.9 to 3.6 per cent carbon, from 1.0 to 2.0 per cent silicon, about .40 per .cent manganese, about .40 per cent phosphorus, about .10 per cent sulfur, from .2 to 3 per cent copper and the balance substantially iron.

4. As an article of manufacture, a chilled copper-bearing material of cast iron analysis of particle size, shape and form suitable for metal blasting, stone cutting and stone polishing characterized by a structure consisting largely of cementite (FezC) and the various transformation products of austenite and having a hardness of at least 550 Brinell, said material comprising 2.9 to 3.6 percent carbon, 1.0 to 2.0 per cent silicon, about .40 per cent manganese, about .40 per cent phosphorus, about .10 per cent sulfur, from 0.20 to 3 per cent copper and thebalance substantially iron.

5. As an article of manufacture, a chilled copper-bearingmaterial of cast iron analysis, of particle size, shape and form suitable for metal blasting, stone cutting and stone polishing, characterized by-improved impact resistance and crushing strength, said material comprising 2.9

to 3.4 per cent carbon, 1.0 to 1.75 per cent silicon, about .40 per cent manganese, about .40 per cent phosphorus, about .10 per cent sulfur, from 0.20 to 3.0 per cent copper and the balance substantially iron.

6. As an article of manufacture, a chilled copper-bearing material of cast iron analysis, of particle size, shape and form suitable for metal blasting, stone cutting and stone polishing, characterized by improved impact resistance and crushing strength, said material comprising 2.9

to 3.4 per cent carbon, 1.0 to 1.75 per cent silicon, about .40 per cent manganese, about .40 per cent phosphorus, about .10 per cent sulfur, from .25 to 1.0 per cent copper, and the balance substantially iron.

7. As an article of manufacture, a chilled copper-bearing material of cast iron analysis, of

particle size, shape and form suitable for metal blasting, stone cutting and stone polishing, characterized by a structure consisting largely of cementite (FeaC) and the various transformation products of austenite and having a hardness of at least 550 Brinell, said material comprising about 3.3 per cent carbon, about 1.3 per cent silicon, about .4 per cent manganese, about .4 per cent phosphorus, about .10 per cent sulfur, about .50 per cent copper, and the balance substantially iron. I

OSCAR E. HARDER. 5o 

